www/rubygem-acts-as-taggable-on: Update from 2.4.1 to 4.0.0

Changelog: https://github.com/mbleigh/acts-as-taggable-on/blob/master/CHANGELOG.md

Also adjust the RUN_DEPENDS to databases/rubygem-activerecord4 and
remove BROKEN_RUBY23 since the new version builds fine with it